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Drilling step and method for improving drilling accuracy

Basic concept of drilling

In general, drilling is a method of machining a hole in a product indication with a drill bit. In general, when drilling a product on a drill press, the drill should complete two movements simultaneously:

1 main motion, that is, the rotary motion of the drill bit around the axis (cutting motion);

2 times to move, that is, the linear motion of the drill bit along the axis direction against the workpiece (feed motion).

When drilling, because of the shortcomings in the structure of the drill bit, it will leave traces on the processed parts of the product, affecting the processing quality of the workpiece, and the machining accuracy is generally below IT10, and the surface roughness is about Ra12.5μm, which belongs to rough processing. .


Drilling operation flow

1. Scribe: Before drilling, first understand the requirements of the pattern. According to the basic requirements of the drilling, use the tool to draw the center line of the hole position. The center line must be clear and accurate, and the finer the better, after the line is finished Measure with a vernier caliper or a steel ruler.

2. Check the square or check the circle: After finishing the line and checking the qualification, the inspection square or inspection circle with the center line of the hole as the center of symmetry should be drawn as the inspection line during the test drilling, so as to check during drilling. And correct the drilling orientation.

3, proofing and rushing: After drawing the corresponding check box or checking the circle, you should carefully sample the eye. First make a small point and measure it multiple times in different directions of the cross center line. See if the punching eye is actually at the intersection of the cross center line, then punch the punching force, round and big, so that it can be accurately The knife is centered.

4. Clamping: Wipe the surface of the machine tool, the surface of the fixture, the reference surface of the workpiece with a rag, and then clamp the workpiece. The clamping is flat and firm as required, and it is convenient to inquire and measure at any time. Need to pay attention to the clamping method of the workpiece to prevent the workpiece from being deformed due to the clamping.

5. Trial drilling: Before the formal drilling, the drill must be drilled first: the horizontal edge of the drill is aligned with the center of the hole to drill a shallow pit, and then the visual inspection of the shallow pit is correct. It is also necessary to constantly correct the deviation and allow the shallow pit to check the circle. Coaxial. If the violation is small, the workpiece can be forced to move in the opposite direction of the violation, and the gradual proofreading is reached.

6. Drilling: Machine-added drilling is generally based on manual feeding operation. When the drilling drilling azimuth accuracy is required, drilling can be performed. When feeding manually, the feed force should not bend the drill bit and avoid the skew of the hole axis.


Drilling accuracy method

1, sharpening the drill bit is the beginning of everything

Before drilling, you should select the appropriate drill bit for sharpening. In addition to ensuring the positive apex angle, the back angle and the traverse angle of the sharpened cutting bit, the length of the two main cutting edges is flat and symmetrical with the center line of the drill bit, and the two main flank surfaces are smooth, in order to facilitate centering and reduce the roughness of the hole wall. The chisel and main cutting edges should also be properly ground (preferably coarsely ground on the grinder and then refined on the stone).

2, accurate line is the basis

Accurately scribe with the height gauge, the first should be accurate and accurate. When scribe, the angle between the scribe angle and the workpiece scribe plane is 40 to 60 degrees (in the direction of the scribe line), so that the line drawn is clear and uniform. To pay attention to the choice of the dash datum plane, the datum surface should be processed accurately, and the flatness of the datum and the perpendicularity with the adjacent faces should be guaranteed. After the hole cross line is drawn out, in order to ensure the easy alignment when drilling, use the center punch to punch out the center point on the cross line (requires the punch point to be small and the position to be accurate).

3, the correct clamping is the key

Under normal circumstances, if the hole diameter is less than 6mm, if the precision is not high, the workpiece can be clamped by hand clamp for drilling; for the hole of 6~10mm, if the workpiece is regular, it can be clamped by the flat jaw, but the workpiece should be made. The surface is perpendicular to the drill spindle. When drilling a hole with a large diameter, the flat-end pliers must be fixed with a bolt presser; for larger workpieces with a drill diameter of 10 mm or more, the platen is clamped by drilling.

4, accurate to find is the key

When the workpiece is clamped, do not rush to drop the drill. There are static alignment and dynamic alignment. The so-called static alignment means that the alignment is performed before the drilling machine is started, and the center line of the drill spindle is aligned with the cross line of the workpiece. This method is relatively easy to grasp for the safety and convenience of the beginner, but the swing of the spindle of the drill is not considered. If the uncertain elements are equal, the drilling accuracy is low. The dynamic search is to find the right after the drilling machine is started. When the alignment is correct, some uncertain factors are taken into account, and the precision is relatively high.

5, careful inspection can not be less

The detection can accurately and timely find the accuracy of the hole so that the necessary measures can be used for compensation. For holes with high drilling accuracy, we generally use drilling, reaming, and reaming. After drilling the small hole in the first step, the caliper is used to detect the deviation of the center of the bottom hole to the reference surface, and the orientation of the bottom hole and the center of the acuity is calculated by the actual measurement. If the loss is not more than 0.10 mm, the hole can be reamed. Appropriately increase the apex angle of the drill bit, weaken the self-centering effect, and compensate the method by appropriately pushing the workpiece in the positive direction and gradually increasing the diameter of the drill tip. If the amount of loss is greater than 0.10mm, the side walls of the bottom hole can be trimmed with an assorted round boring tool, and the trimming portion should be connected with the arc smooth transition of the bottom hole.

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